Internet comprises over 100 billion plus web pages on over 100 million websites being accessed by nearly 3 billion users conducting approximately 3 billion Google searches per day, sending approximately 150 billion emails per day. With statistics like these the data being uploaded and downloaded every second on the Internet is staggering even before considering the expected growth of high bandwidth video in mobile applications etc. In 2016 user traffic is expected to exceed 100 exabytes per month, over 100,000,000 terabytes per month, or over 42,000 gigabytes per second. However, peak demand will be considerably higher with projections of over 600 million users streaming Internet high-definition video simultaneously at peak times.
All of this data will flow to and from users via data centers and across telecommunication networks from ultra-long-haul networks down through long-haul networks, metropolitan networks and passive optical networks to users through Internet service providers and then Enterprise/small office—home office (SOHO)/Residential access networks. In the long-haul national and regional backbone networks and metropolitan core networks dense wavelength division multiplexing (DWDM) with channel counts of 40 or 100 wavelengths supporting 10 Gb/s and 40 Gb/s data rates per channel have been deployed over the past decade and are now being augmented with next generation 40 Gb/s and 100 Gb/s technologies for ultra-long-haul, long-haul and metropolitan networks.
Historically, the optical layer within telecommunications networks has been simplified for transmission with data processing performed in the electrical domain. Essential in each of these optical communication links is the photodetector (PD) within the receiver front-end for converting the received optical signal into the electrical domain. Moreover, the overwhelming majority of optical receivers employ a transimpedance amplifier (TIA) in conjunction with the photodetector in order to amplify the received electrical signal as well as convert the photocurrent into a voltage wherein subsequent decision/error correction circuits etc. regenerate the electrical data. In the ongoing drive for increased performance, reduced cost, etc. materials such as silicon-germanium (SiGe) are being explored as promising candidates for photonic integration of the photodetector functionality with the front end TIA electronics for high bandwidth/data rate communication links. However, an important consideration is the bandwidth mismatch between the optical PD and the electronic TIA circuit. For example, whilst the bandwidth of a SiGe PD can be extended up to 60 GHz through exploiting inductive gain the provisioning of suitable TIAs at such bandwidth remains challenging.
Photonic integration exploiting standardized silicon photonic processes has evolved to the level that permits affordable fabrication of complex optical systems. Accordingly, new paradigms and architectures can be exploited to either optimize optoelectronic devices or support processing in the optical domain to ease the performance requirements of the front end electrical components and processing circuits with anticipated reductions in the cost and/or the power consumption of these electronic circuits.
To date the focus of photonic integration has been primarily towards parallelism within the optical domain through wavelength division multiplexing (WDM) or exploiting the dual polarizations within optical waveguides. However, in many architectures “brute-force” time division multiplexing (TDM) offers benefits through reduced complexity and cost. Despite this photoreceivers either in discrete or optical waveguide forms are primarily the same now for 10 Gb/s, 20 Gb/s and above TDM as they were 20 or 25 years ago. Accordingly, it would be beneficial to provide optical circuit designers with a new approach allowing them to exploit the inherent high TDM capabilities of optical links without resorting to expensive electronics but leveraging high speed CMOS and other integrated circuit methodologies.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.